Enthalpy and Internal Energy relationship

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Kevin Chang 2I
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Joined: Mon Jan 04, 2016 9:16 am

Enthalpy and Internal Energy relationship

Postby Kevin Chang 2I » Sun Jan 22, 2017 11:37 pm

How does the change in internal energy relate to a change in enthalpy and why (or when) is it necessary to convert values of delta(U) into delta(H)?

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Joined: Fri Jul 15, 2016 3:00 am

Re: Enthalpy and Internal Energy relationship

Postby Angela_Pu_3C » Mon Jan 23, 2017 2:10 am

The change in internal energy(ΔU) is a a combo of energy transferred from heating(q) and compression(w). When at a constant pressure, q can be equivalent to the change in enthalpy(ΔH), being heat released or absorbed at constant P. So increasing/decreasing ΔH will inc/dec ΔU accordingly. When the rxn is at constant P and has insignificant PΔV (no changes in #of moles of gas), ΔU will equal ΔH bc no w is done, and the only energy transferred is that of heat. For why/when you'll need to "convert values of ΔU into ΔH" I'm guessing it'll be when you're given a ΔU and other info for a rxn and you're asked for the ΔH, which you'll get by plugging into ΔU=ΔH-PΔV.

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